Well Intrepid Ibex is out, and if you're a fan of Ubuntu you are probably champing at the bit to get your hardy install(s) up to the next release. Unfortunately, you're going to be competing on bandwidth with millions of others who want to do the same thing.
A clean install of Kubuntu requires just over 1 GB of packages to upgrade from Hardy to Intrepid, and dragging that much data across the cloud is just painful, I don't care how fast your ISP is. It's especially painful if you happen to have an apt-mirror server on your own LAN with a full copy of the Intrepid repository.
With Debian, of course, upgrading is just a matter of changing to the next release in /etc/apt/sources.list and doing aptitude dist-upgrade. With Ubuntu, that doesn't work out so cleanly (though I can attest that it does work if you're willing to hack around on it a bit). You have to use the do-release-upgrade script instead.
So enough pointless rambling, how do we get do-release-upgrade to recognize our local apt-mirror server? Do read on...
1. First, our apt-mirror needs to have Intrepid downloaded. I mirror all of ubuntu, ubuntu-backports, ubuntu-updates, and ubuntu-security on my server, with main, restricted, multiverse, and universe. You probably need Hardy on there as well, but if you've got a server like this you probably already do.
2. On your clients, if you've manually added your local server and it shows up in Synaptic as a "third party software" server, delete those entries. Close out of synaptic.
3. Open the file /usr/share/python-apt/templates/Ubuntu.mirrors. Add in the URL of your own apt-mirror server. I added mine under the US heading, but it probably doesn't matter. Make sure you use the full path to the root of the mirror (e.g. http://myserver.mydomain.foo/ubuntu/).
4. Now open Synaptic again. On the repositories dialog, click on the "download from" dropdown and select "other". You should get another dialog with a list of servers, and your server should be on this list now. Select it.
5. Make sure you have checked the boxes for the various sections of Ubuntu you want to receive (updates, security updates, etc).
Now, do-release-upgrade should recognize your lan server. That GB of files should download in no time!